An introduction to energy and its importance?

Introduction to energy

Energy
makes things happen. Nothing could live
or move without energy. Plants and trees
need energy to grow, animals use energy to walk or run, cars and trains need
energy to run. Energy lets us do things
such as playing a game or climbing a hill.
In fact, nothing can happen without energy.

What is energy?

The
world we live in is full of energy.
Light and heat are forms of energy.
Electricity is a form of energy. Energy is commonly known to exist in
several forms. Almost everything can be traced to the use of one form or other.
You are reading this only because light energy reaches your eyes, this light
energy being activated by the electrical energy supplied to your computer and
the electrical energy being generated from mechanical, hydel, combustion, solar or nuclear energy.

Most energy comes from the sun. It provides heat and light for plants to
grow. Chemical energy is energy stored
in chemicals such as fuel. Even these
fuels such as coal and petroleum were made from plants which absorbed the sun's
energy millions of years ago.

The
academic definition of energy describes it as the capacity to do work. The importance of energy in life or in physics
is certainly not as simplistic as its definition. It is all-pervasive,
omnipresent and fundamental to every phenomenon. Physics recognises this in
many, many ways.

A
scientific approach to an understanding of energy,
requires an understanding of the term force,
the work done by the force, and
the power
needed to do that work.

What is Force?

We
commonly understand that a force is needed to push or pull an object. Let us do
the following imaginary experiments to
understand it better:

Imagine
you give a push to a light plastic chair. It moves very fast! It has
'accelerated' to this speed from rest. Now, imagine you are pushing your study
table. With the same effort, the table hardly moves! You need to exert more -
apply more force - to push this 'as fast as the chair'.
What
do you infer? A light object moves 'faster' than a heavy object under similar
pushes or forces. Do more such experiments. You will notice that as the object
grows heavier it is more sluggish for the same force. Would you ever imagine an
elephant darting across like a deer in the zoo?

Putting
it more compactly, the more massive
an object is and/or faster the object
has to move, more is the force needed. A simple formula can be generated from
this statement:

Force(F) = mass(m) X
acceleration(a)

Sir Isaac
Newton proposed the characteristics of force as
follows:

1. Every body persists in its state of rest or
of uniform motion in a straight line unless it is compelled to change that
state by force(s) impressed on it.

2. The rate of change of momentum of a body is proportional to the resultant force
acting on the body and is in the direction of the force. (This statement leads
to the formula F = ma . Can you find out how?)

3. To every action there is always opposed an
equal reaction; or, the mutual actions of two bodies upon each other are always
equal, and directed to contrary parts.

In
essence, force can cause bodies to move.
If a body is already moving, it may alter its speed or its direction of
motion or else bring it to rest. Hence
force is that which changes a body's
state of rest or of uniform motion in a straight line.

What is work?

Commonly,
the term 'work' refers to some physical activity. It involves some kind of motion
-the motion of hands when you write, of eyes when you read, of mouth when you
eat or talk etc. If your two-wheeler had failed you on your way back home, you
know how much 'work' you had to do pushing it to the nearest mechanic. If you
don't move anything - not even 'lift your little finger' - you are an idler,
that is, you don't do any 'work'!

Physics
defines work as that which is done
by a force. A constant force F
acting on a mass m provides to it a motion with acceleration a. Whether the body
moves through 1 meter or 1 km under ideal friction-free conditions the force
required is the same if its state of motion (say, its speed) does not change.

Does
it mean then that moving the body by 1 meter or by 1 km. are equivalent? Can't
be, certainly. The force required to set in either of the movements above may be the same, but the work
done (and hence, the energy spent) in the two cases are different. Sounds
logical, doesn't it?

Work done by a force F on a particle
thereby moving it through a distance d in a straight line in its direction, is
given by W= Fd, a product of force and
distance. This implies that if the force does not move the particle, no work is
done.

Units:
One joule ( also called Newton-meter) of work is done by a force of one Newton
in moving the particle by one meter (SI system).

One
erg (also called dyne-cm) of work is done by a force of one dyne moving the
particle through one centimeter (cgs system).

1 joule =10^7ergs.

Work
done by particles like atoms, electrons etc. are measured in terms of 'electron
volt' (eV), which is as small as 1.6X10^-19 joules.

You
would have realised that the motion of a particle (body) is not properly
described unless its speed and its direction of motion are specified. Similarly
force as well as the acceleration it produces has to depend on its direction.
When you enter your house you push the door open and when you leave your house
you pull it shut. The forces in the two cases may be same in value or 'magnitude'
but opposite in 'direction' to each other. Remember, the two forces are
not equal!

What is power?

Power
is the rate at which work is done. If different parts of a work are carried out
at different rates then an average power can be defined.

Power(P) = Work done(W) / time taken(t)

Units:
In the SI system the unit of power is joule/sec. It is also called one watt
(in honour of James Watt of steam-engine
fame).

A
'horse power' (used for rating
automobilies) is a unit equivalent to 550 ft. pound/sec. It takes 746 watts to
deliver one horse power (hp or BHP).

Watt
and its higher denomination namely kilowatt (=1000watts) is so popular that
work is often defined from power as watt-hour
or kilowatt-hour (kwh) because after
all work is power x time. Our
domestic electricity usage is measured in kwh even though it is popularly
referred to simply as 'unit'!

Work Energy Theorem

We
know that energy is needed in order to carry out work. In one sense, energy is
perceived as a store-house which is expended as work when called for. This idea
is given shape in the following explanation of the 'work-energy theorem' which
is fundamental to physics.

Imagine that a particle (or object) of mass m is
given a push by a force F thereby accelerating it . The acceleration a (= F/m)
is defined as the rate of change of
velocity ( speed with direction). If the particle which was moving with a
velocity vo speeded up to v due to the force in a duration
of t seconds then

a = ( v - vo) / t

In
order to calculate the work done in the above motion, we need to know the
distance by which the particle was pushed.
If the motion was smooth, the distance moved is simply the product of
the average velocity (i.e. speed) and the time taken for this motion.

Let
us use s to denote this distance. Then,

s = ( v + vo ) t / 2

since
the average speed is ( v + vo) / 2.

Work
done by the force F in the above 'job' is obtained as

W = F s =
m a s = m ( v - vo) ( v + vo ) / 2

= 1/2 mv^2 - 1/2 m vo^2

If
the particle was at rest when the force moved it vo = 0 and the work done is simply 1/2 mv^2. That is, the
particle 'possesses' a work equivalence of 1/2 mv^2 due to its motion. Let us call this its energy
- rather 'kinetic energy' (kinetic refers to motion) - which will propel and
sustain its motion as long as it does not lose it by doing work against
friction . If the particle was already moving, the force produces a change in
its kinetic energy of value 1/2 mv^2 - 1/2 m vo^2 .

The kinetic energy of a particle is given by 1/2 mv^2.

Measuring Energy

Energy
is measured in units called Joules (J).
The joule is a small unit. A
kilojoule (KJ) is 1000J. This is the
unit used for measuring the amount of energy in our food. Kilocalories (Kcal) also may be used.

One Kcal = 4.2 KJ

Energy sources - Historic

The
prehistoric man who existed about 50,000 years ago was a wild man, who lived in
caves in jungles in conditions similar
to other animals. He wandered from place
to place in search of food and shelter.
The main source of energy at his disposal was his own internal
energy. This is called Muscular
Energy. Of course, even today this form
of energy is utilised by human beings.
In running, jumping, lifting objects etc. man uses this energy. Muscular energy is obtained from the food we
eat.

The
first external source of energy was fire, which was used for heating, lighting
and cooking. The fuel used for getting
fire was initially wood. Later coal and
peat became major sources. Over a period of time man learnt to harness
different forms of energy to increase his ability to do work.

Energy sources

The
sun is the most important source of energy.
More energy reaches the earth from the sun in an hour than all of us use
in a year. Apart from direct solar
energy, the sun's energy shows in different ways - wind power, water power, tidal power, fossil
fuels, nuclear energy, etc

Man
has discovered many sources of energy and he goes on attempting to discover
more sources and to use them to make his life more comfortable. In our day to day life we use a lot of
energy. The lights in our homes,
offices, water heaters, cars, planes,
trains etc. use up a lot of energy. Thus
our modern civilisation is heavily dependent on the availability of energy.

FORMS OF ENERGY

Energy exists in several forms. Whenever work is done energy is converted from one form to another.Energy conversions are happening all around us. When you switch on an electric light, electrical energy is converted into light and heat energy. In a telephone, sound energy is converted into electrical energy and at the other end electrical energy is converted back into sound energy.

Energy exists in several forms. Some of the important forms are

Biological & Chemical energy.

Mechanical energy (kinetic and potential energy)

Heat energy.

Light energy

Electrical energy

Sound energy

Nuclear energy

Chemical energy

Solar energy

NEED FOR ENERGY

All living organisms need energy-

1. To carry out natural movements and other physiological functions - like respiration, digestion, circulation etc.; we get energy from the food we consume

3, For industrial use - Electrical energy is needed for industrial use. This energy is used for illuminating work places, for heating furnaces and running electric motors and various other machines. Fuels such as coal, furnace oil, bagasse and wood are used for heating purposes. Electromagnets are used in cranes for lifting and shifting heavy loads of iron.

4 For agriculture - Man and animal power is needed for agricultural activities. Tractors, threshing and winnowing machines are now used very extensively. They require fuel energy. The pumps used for drawing water from wells or canals run on electricity or on diesel.

5. For transport - In early days, man used muscular energy for travelling from place to place. Later he harnessed powerful animals like bullocks, house donkeys etc., which he used for drawing carriages. Today man uses fast moving vehicles like aeroplanes, buses, cars, trucks etc., which run on fuel energy. He also uses electric trains which require electrical energy and steam cars that run on steam energy.

The amount of energy consumed by a country depends upon the life styles of its people and the processes by which it produces goods and services. These factors depend upon the technological developments of that country. Generally technologically advanced countries seem to consume larger amounts of energy.

The United States uses the most energy followed by the C.I.S and Western Europe. India , though having about 15 % of the world population consumes only about 2 % of the total energy in the world.

THE ENERGY CRISIS AND CONSERVATION OF ENERGY

Our modern civilisation is heavily dependent on the availability of energy. Conventional sources of energy such as coal , mineral oil, natural gas and atomic materials are limited in their supply and could be exhausted one day. The currently known reserves of oil and gas deposit may last only 30 years. Coal fuel may last for a couple of centuries.

Can we imagine a time when we may not be able to use all the material comforts we are used to, because of an energy crisis? Thus the importance of energy conservation cannot be overstated.

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